Constitutionalization on a Spectrum: Balancing Sovereignty and Integration in Eurasia (EU,EAEU,and ASEAN Compared)

Abstract

This article examines the phenomenon of constitutionalization in regional integration entities, arguing that the adoption of constitutional-like frameworks is a pivotal process for ensuring their sustainable development and effective operation. Through a comparative analysis of the European Union (EU), the Eurasian Economic Union (EAEU), and the Association of Southeast Asian Nations (ASEAN), the author conceptualizes constitutionalization not in its classical state-centered sense, but in the much broader sense as a spectrum of legal institutionalization and consolidation. This spectrum ranges from the supranational model, characterized by a hierarchical legal order and primacy of common law (EU), to the intergovernmental model, based on strict sovereignty preservation and consensus (ASEAN). The EAEU occupies a hybrid middle ground, strategically balancing economic integration with strong safeguards for national sovereignty. The paper concludes that constitutionalization, understood in this broad, non-traditional sense, is not a uniform process but must be adapted to each region’s unique political, historical, and economic context. It offers insights into how regional integration entities can selectively adopt advanced legal and institutional tools—such as dispute resolution mechanisms, qualified majority voting, and legal harmonization—to enhance functional efficacy and resilience, thereby contributing to their long-term sustainability and effective governance.

Introduction

This article employs an expanded analytical framework of “constitutionalization.” It moves beyond the classical theory of the state constitution to examine how regional integration entities develop advanced, consolidated legal orders that perform foundational, constitutive, and constraining functions analogous to—but distinct from—national constitutions. This process of profound legal institutionalization is a critical factor in ensuring the stability, legitimacy, and effective operation of such entities. Their constitutive instruments prioritize general principles of organization and functioning, governing the interaction between the entity and its member states. These principles simultaneously safeguard the entity’s foundations and operational efficacy, while respecting the sovereign status of member states. Rather than being created ex nihilo, these principles draw upon existing international and national legal principles, adapted to the entity’s specific organizational needs. The fundamental principles governing the EU’s political power are increasingly exhibiting constitutional characteristics (Chetverikov, 1999, p. 15).

While the EU serves as an excellent example of deep legal institutionalization at the supranational level, there are organizations pursuing integration at differing levels of legal cohesion. For example, the ongoing integration process of the Association of Southeast Asian Nations (ASEAN) and its Community functions with a distinct, consensus-based intergovernmental logic; nonetheless, its foundational document performs a constitutive, framework-setting role. The Eurasian Economic Union (EAEU), established by treaty in 2014 as an international organization for deep economic integration in the post-Soviet space, presents a third model. It differs significantly from the European Union in its goals, principles, and operational parameters. Consequently, the EU’s model of legal integration is not directly applicable to the EAEU. However, certain EU-developed technical tools for legal ordering could prove valuable in addressing the EAEU’s current challenges of self-definition, consolidation, and international projection (Voinikov et al., 2019, p. 95). In this regard, the more flexible, sovereignty-conscious model of the ASEAN Community could also serve as a useful reference point. For the purposes of this article, the term “regional integration entity” is used as an umbrella, functional category that encompasses both regional organizations sensu stricto and regional integration settings. The European Union is treated as a supranational regional integration entity whose legal order goes beyond a conventional international organization, the Eurasian Economic Union is approached as an international organization for regional economic integration with a deliberately hybrid institutional design, while ASEAN is considered an intergovernmental regional organization whose Community structure represents a comparatively modest, sovereignty-preserving integration setting. This analytical clarification allows for consistent use of terminology throughout the paper and avoids conflating distinct organizational logics.

This paper starts by briefly introducing the theme of examining the advanced legal institutionalization—conceptualized here as “constitutionalization”—of integration legal orders. Part 2 elaborates on this conceptual framework, acknowledging its departure from and dialogue with classical constitutional theory. The examples of the EU, the EAEU, and the ASEAN Community are examined in Parts 3, 4, and 5, respectively, with a focus on how their legal frameworks contribute to sustainable development and effective operation. Part 6 offers an in-depth analysis of the opportunities and prospects for the use of constitutional tools. Given the comparatively higher degree of legal consolidation and the richness of both primary law and case law, the EU necessarily occupies a more prominent place in the empirical analysis. The EU’s supranational legal order, centered on the TEU and the TFEU and interpreted by the Court of Justice of the EU, provides the most developed example of advanced legal institutionalization and thus serves as the primary benchmark for the spectrum of constitutionalization. The EAEU and ASEAN are discussed in a more concise manner, yet their respective hybrid and intergovernmental models are analyzed precisely in relation to, and sometimes in deliberate contrast with, this EU benchmark. The paper concludes that a process of advanced legal ordering is a pivotal, though varied, process for international integration entities to ensure their proper functioning and long-term resilience.

Conceptualizing Constitutionalization: From National Roots to Supranational Aspirations

The discourse surrounding the constitutionalization of international and regional legal orders is characterized by profound conceptual diversity and scholarly debate. At the outset, a crucial clarification is necessary: this article employs the term “constitutionalization” in a specific, functional, and non-classical sense that deliberately diverges from its orthodox meaning in traditional constitutional theory. Classical constitutionalism, born of the late 18th-century revolutions in North America and France, is intrinsically tied to the sovereign nation-state. It conceives of a constitution as the supreme, foundational legal act of a state, establishing its fundamental political structure, distributing powers, and guaranteeing individual rights against public authority. Applying this term to non-state entities such as the EU, the EAEU, or the ASEAN inevitably stretches its semantic boundaries and has been met with justified skepticism by scholars of constitutional and state theory, particularly those emphasizing the state-centered foundations of constitutionalism (Gouaud, 2003; Grimm, 2012; Isensee, 1995; Kirchhof, 1999; Schmitt, 1928). To preempt confusion and acknowledge this theoretical divergence transparently, this analysis uses “constitutionalization” synonymously with the process of advanced legal institutionalization and consolidation within an international organization. It denotes the progressive development whereby an entity’s founding treaties and legal practices acquire characteristics and functions analogous to a constitution: they define the organization’s legal personality, structure its governance, vertically and horizontally distribute competences, establish a hierarchy of norms, encode fundamental principles, and provide a framework for resolving legal disputes. This broad, functional understanding, while controversial, serves as a valuable heuristic tool for comparing the depth, nature, and operational logic of different regional integration projects beyond the confines of the state paradigm.

Scholars offer varying perspectives on this phenomenon. Some posit that national constitutional norms directly influence and are reinforced within the framework of interstate entities, citing the drafting of the EU Constitution (or, more accurately, the Treaty of Lisbon) as an example (Battini, 2006, pp. 35–40). However, this view can overlook the complex interplay of power and negotiation inherent in treaty-making. Others more comprehensively define constitutionalization as the process whereby the principles and norms of various national constitutional laws cumulatively shape the legal order of an interstate entity (Schimmelfennig, 2018, p. 975). The adoption of international treaties containing supranational norms possessing characteristics akin to constitutional norms—such as direct effect, primacy, and binding force, exemplified by the Treaty of Lisbon—signifies a significant development. Yet, describing this as a “new vector of dialectical development” is arguably too deterministic. It is more accurate to characterize it as a complex and evolving process whereby national constitutional traditions interact with the developing legal order of international organizations, often resulting in tension and negotiation between national sovereignty and supranational authority (Goudappel, 2010, p. 40).

The increasing incidence of duplication and conflict between international, regional integration, and national legal systems has spurred doctrinal discussion regarding the “constitutionalization” of the international legal order. This approach seeks to address the multidimensional and complex interplay between these three legal orders. While diverse constitutionalist perspectives exist, differing in their premises and methodologies, they generally converge on the need for, as de Búrca suggests, “a systemic unity governed by an agreed set of ground rules and principles for the global sphere” (cited in Goudappel, 2010, p. 42). However, legal pluralism simultaneously emphasizes the inherent diversity characterizing the interaction of these systems. National constitutional law acts as a crucial filter in the implementation of international and regional integration law, mitigating potential negative consequences and ensuring domestic legislation aligns with common international standards, legal principles, and established channels of influence. This filtering role, however, varies dramatically depending on the nature of the integration project. In the European Union, for instance, the classical understanding of a national constitutional “filter” does not apply, as EU law enjoys primacy over the national laws of its Member States, including their constitutions (Court of Justice of the EU, 1964, Case 6/64, Costa v ENEL). This doctrine, established by the European Court of Justice, dictates that in the event of a conflict between an EU regulation and national constitutional provisions, EU law must prevail and be applied, effectively overriding conflicting national norms. The only widely acknowledged, albeit contested, exception to this principle arises when EU law is found to infringe upon the core constitutional identity of a Member State—those fundamental political and constitutional structures that define the state’s very essence (Article 4(2) of the Treaty on European Union). This principle of “identity review” was famously articulated by the German Federal Constitutional Court in its Solange I decision (BVerfG, 1974), where it asserted its right to review the compatibility of EU law with the fundamental rights guaranteed by the German Basic Law, though it has since conditionally accepted the primacy of EU law as long as the EU ensures an equivalent level of fundamental rights protection. Such a dynamic, where a supranational legal order can directly override national constitutional provisions except in matters of “core identity,” is a unique feature of the EU and would be inconceivable within the legal frameworks of the Eurasian Economic Union or ASEAN, where national sovereignty remains far more absolute and less encroached upon by the supranational center. This supranational configuration is grounded in the primary law of the Union itself, in particular in the Treaty on European Union and the Treaty on the Functioning of the European Union as amended by the Treaty of Lisbon, as well as in the case law of the Court of Justice (e.g., Costa v ENEL).

Constitutionalization, in the broad sense used here, is a multifaceted process encompassing two key aspects: aligning social relations within the integration entity with higher-order legal requirements and applying constitutional principles and norms across the developing branches of its law. This involves imbuing the entity’s policies, legal doctrines, and various legal fields with constitutional prescriptions, ultimately aiming to harmonize public relations at all levels—including the supranational—with the spirit and letter of foundational norms. Distinguishing between the constitutionalization of domestic and international legal orders is crucial. Domestic constitutionalization elevates the Basic Law’s influence across societal spheres, while international constitutionalization focuses on the legal orders of international integration entities. This highlights the timely need to explore effective methods of such legal consolidation.

Classical constitutional theory, when analogically applied, posits two primary methodological approaches to consolidating a legal order, reflecting the degree of integration of foundational norms within a system. These approaches, while initially described in the context of domestic legal orders, possess relevance for both domestic and international (including supranational) systems. The first is normative-legislative constitutionalization. This traditionally involves elevating ordinary legal norms to constitutional status. However, this approach is limited if the constitution itself delineates specific subject matters reserved for constitutional laws. Furthermore, even if successfully implemented, this method does not guarantee a harmonized legal system. Constitutional laws, even if elevated in status, remain distinct from the core constitutional text and cannot alter its provisions. The resulting legal landscape may contain potentially conflicting norms of differing legal force. The second is normative-interpretative constitutionalization, achieved through the interpretive activities of a constitutional court during constitutional review. This approach relies on the court’s interpretation of the constitution and its application to specific cases involving potentially unconstitutional legislation. Several characteristics distinguish this method. First, it is inherently reactive, addressing constitutional conflicts as they arise. By resolving these disputes, the court fosters consistent application of the constitution by state bodies, especially lower courts. Second, it offers a flexible means of harmonizing national legislation with the constitution’s spirit and principles. However, this is a gradual, long-term process, reliant on litigation rather than proactive court initiative. Third, it carries the risk of altering the substance of constitutional norms without formally amending the text, potentially leading to unintended expansions or modifications of original constitutional intent. In the context of regional integration, these processes translate into treaty amendments (legislative) and the jurisprudence of bodies like the Court of Justice of the EU (interpretative).

The increasing influence of constitutionalism on the development of the international system is evident in the modern era. This influence facilitates the formation of stable, integrated legal orders within specific regions (Romashov, 1998, p. 67). A notable trend is the constitutionalization of international law, driven by the incorporation of constitutional law’s norms, principles, and doctrines. This is exemplified by the constitutions of the European Union and the Union State of Belarus and Russia (Union State, 1999). The consolidation of human rights and freedoms, along with their protective mechanisms and other constitutional institutions, represents a key aspect of this process (Isaev, 2003, p. 215). Constitutionalization of international and integration law can thus be understood as the impact of contemporary constitutionalism and the constitutional law principles and norms of various states on the normative frameworks of both international and integration law. Consequently, integration law is increasingly shaped by constitutional principles, acquiring a more universal foundation for its continued development within the context of interstate integration.

The genesis of proposals for a world constitution can be traced to the burgeoning European constitutionalism of the early nineteenth century. Jeremy Bentham’s Leading Principles of the Constitutional Code for Any State exemplifies this early advocacy for international legal internationalization through a global constitutional framework (Bentham, 1823, p. 1). These ideas found further development in the twentieth and twenty-first centuries within various theories of the constitutionalization of international law, notably those articulated by Walter Hallstein and Hermann Mosler (Mosler, 1999, p. 305). These scholars highlighted the mutually reinforcing relationship between constitutional institutions and international law, arguing that this interaction strengthens and legitimizes the international legal order, fostering interstate integration. However, contemporary constitutionalism exhibits a countervailing trend: a diminished role for constitutional law, a departure from traditional constitutional doctrines and conservatism. This trend contributes to significant instability in the constitutional development of individual states, as exemplified by the United Kingdom’s withdrawal from the European Union. Addressing this instability, some scholars propose the eventual emergence of objectified, global principles of constitutionalism (Kovler et al., 1996, p. 89).

Some scholars posit that certain universal norms of international law fulfill a constitutional function, impacting not only international but also domestic legal orders. This function, he argues, is twofold: to maintain international peace, security, and legality among states, and simultaneously to safeguard human rights and the rule of law within individual states, ultimately benefiting the individuals who are the ultimate beneficiaries of international law. Furthermore, Tomuschat contends that the traditional role of international law in regulating interstate relations is now complemented by both a constitutional function and functions analogous to those of national administrative and private law. He characterizes contemporary international law as a “universal template for social life” (Tomuschat, 1999, p. 162), a multifaceted system pervading all spheres where governments act to protect the public interest, effectively constituting a “common legal order for humanity as a whole.” This perspective challenges the traditional dichotomy between international and national (constitutional) law, replacing it with a conception of an integrated, multi-level legal system where both systems are interconnected and interdependent, rather than discrete and separate spheres (von Bogdandy, 2012a, pp. 22–23).

The assertion that a constitutionalized international and integration legal order is achievable merits consideration. Evidence of this potential is found in the increasingly palpable processes of constitutionalization within international and integration law. However, it is crucial to acknowledge that states often make legal decisions—such as the UK’s accession to the EU—without fully anticipating the subsequent ramifications for their national constitutional law and doctrine (Galushko, 2023, p. 247; Kodaneva, 2005, p. 22). This highlights the complexity inherent in such a transition. While the notion of a constitutionalized international order may appear particularly utopian against the backdrop of contemporary geopolitical tensions, it nonetheless reflects a strand of thought in constitutionalist scholarship that, in the early twenty-first century, considered such a development a conceivable—albeit contested—trajectory for the evolution of international law. Habermas’ critique of viewing international relations solely through a Hobbesian “state of nature” lens is particularly relevant. The prevalence of constitutional democracies among key international actors suggests that constitutional principles already influence their actions on the global stage (Habermas, 2008, p. 125). Therefore, the shift toward a global institutional order safeguarding core constitutional principles might be less arduous than escaping a Hobbesian state of nature between individuals. International constitutionalism, in this context, represents not a radical departure but rather a natural extension of domestic constitutionalism and a further step in societal progress (Habermas, 2008, p. 130).

The concept of “supranational constitutionalism” describes two interconnected processes of systemic legal regulation and, in its prevailing usage in legal scholarship, is typically reserved for non-state but state-like entities such as the European Union (e.g., Habermas, 2012). First, it encompasses the constitutional and legal framework governing states’ participation in integration processes. This involves, first, the constitutional recognition of specific social relations requiring higher-order regulation, thereby expanding the scope of constitutional authority. Second, it leverages multi-level constitutional legislation to influence the entire national legal system, minimizing the need for frequent constitutional amendments. Legal innovations can be integrated at various levels, thereby transforming national law without constant constitutional revisions. This constitutionalization extends beyond national law and encompasses international and integration law. Defining the constitutionalization of EU law presents a challenge, as applying constitutional principles to a supranational entity like the EU, blending state and international organization characteristics, is complex. While direct application of national constitutional principles is problematic, comparisons are primarily drawn with national models, accounting for the EU’s unique legal order. It is within this nuanced, expanded, and functionally-oriented understanding of constitutionalization as advanced legal institutionalization that the subsequent comparative analysis of the EU, EAEU, and ASEAN will proceed. This framework allows us to examine the spectrum of how these entities organize their legal and political space, balance sovereignty and integration, and strive for sustainable development and effective operation through the consolidation of their foundational legal frameworks.

Anatomy of a Supranational Polity: The EU's Constitutional Architecture

The European Coal and Steel Community (ECSC), the precursor to the European Communities and subsequently the European Union, benefited significantly from the advocacy of the federalist movement. This movement championed the integration of Western European powers, envisioning a gradual progression from partial unification to a confederation, and ultimately a federation akin to the United States of Europe. Federalist ideals profoundly shaped the EU’s institutional architecture, operational mechanisms, and stated objectives, as evidenced by the founding treaties’ emphasis on “an ever closer union among the peoples of Europe” in Article 1(2) of the Treaty on European Union (TEU) (European Union, 2012a).

However, while the explicit rhetoric of federalization has diminished within the EU—potentially due to societal divisions and political tensions—the underlying pursuit of federal characteristics has persisted. The EU has consistently striven to enhance its federal attributes, strengthening interstate relations and the relationship between member states and EU institutions, while respecting the full sovereignty of member states within the international legal order. This pragmatic approach continues, alongside ongoing calls for a more explicitly federalist EU, often framed as the creation of a “single European democracy.” Proponents of pan-European integration frequently advocate for the establishment of transnational European parties and the implementation of pan-European electoral lists for the European Parliament as a crucial next step (van Lanschot, 2021).

The period spanning the late 1990s and early 2000s witnessed a significant shift in the European Union’s trajectory. Concurrent with the EU’s rapid, albeit somewhat haphazard, expansion, efforts toward greater integration intensified, culminating in proposals for constitutionalization. This culminated in the convening of the Convention on the Future of Europe. While the resulting draft EU Constitution failed referendums in France and the Netherlands (Startin & Krouwel, 2013, p. 65) and was subsequently abandoned in favor of the Treaty of Lisbon, the latter, effectively achieving a form of profound legal consolidation, was subsequently adopted by member states. This circumvented direct democratic approval, however, and resulted in a unique system lacking the full panoply of attributes traditionally associated with federal statehood.

First, a significant power shift occurred. Disparate national elites ceded considerable authority to a newly emergent supranational elite. The ramifications of this transfer became starkly evident during the Eurozone crisis. The Greek government’s attempt to pursue an independent economic policy, including the announcement of a referendum on the terms of the third financial assistance package and proposals to renegotiate the conditionalities attached to the bailout, diverging from the preferences of key decision-makers within the Eurogroup, the European Commission and the European Central Bank, met with swift and decisive action. Faced with the threat of financial collapse and expulsion from the Eurozone, Greece was compelled to accept the bailout conditions imposed by its creditors, including the Eurogroup, the European Commission acting within the so-called “Troika,” and the European Central Bank (Entin & Entina, 2015, pp. 230–245). These conditionalities were formalized in assistance programs agreed within the framework of the European Stability Mechanism (European Union, 2012b).

The Treaty of Lisbon enshrined a principle of power distribution reminiscent of federal systems, particularly Germany’s, wherein member states retain all powers not explicitly transferred to the supranational level. Legislative autonomy remains within this defined sphere (Borchardt, 2018, p. 27). The EU’s founding treaties, though formally international legal instruments, function effectively as a written constitution. They occupy a position of supreme authority within both the supranational and national legal orders, superseding conflicting national or EU legislation (Court of Justice of the EU, Case 6/64, Costa v ENEL, 1964). Violation of these treaties incurs legal and material consequences.

The European Union, since its inception, has fostered a culture of conscientious application of supranational law, integrated into national legal frameworks. While Eastern and Southeastern European member states continue to adapt, a robust multi-level system of enforcement has emerged. Uniquely, this system relies heavily on individuals and businesses—EU citizens and companies—to drive enforcement, rather than solely on government agencies or the EU bureaucracy. Furthermore, the European Commission, acting as the EU’s executive, mediates disputes arising from breaches of supranational law, preventing escalation into interstate conflicts and prioritizing the common interest (European Commission, 2021).

The EU’s legislative process operates in a “crowding out” manner, progressively restricting member states’ independent legislative powers. Where the EU holds exclusive competence, member states lose the ability to regulate the relevant area upon delegation of power to the supranational level. Similarly, under regimes of shared competence, member states forfeit their individual regulatory right once jointly developed and adopted legislation enters into force, even if approved by a qualified majority rather than unanimously (Borchardt, 2018).

The assertion of uniform application of supranational law throughout the EU, without exception, requires qualification. While the Court of Justice of the EU (CJEU) plays a crucial role in ensuring consistent interpretation and application of EU law, the reality is a more nuanced system of judicial cooperation between national and EU courts. A complete “merger” into a single judicial system is inaccurate. Instead, a system of preliminary rulings and mutual recognition fosters convergence, though divergences in national judicial practice remain. The assertion that the CJEU functions as the highest constitutional, supreme, and administrative court of both the EU and its member states is also an overstatement, even though parts of the literature occasionally employ language that comes close to such a characterization (e.g., von Bogdandy, 2012b, p. 322). Its jurisdiction is limited to EU law, although its interpretations significantly impact national legal systems. The analogy of a “common market for judicial decisions” is useful, though its formation is ongoing, not necessarily in its final stages. The CJEU’s role in ensuring the uniform application of EU law is undeniably crucial for creating a stable and predictable business environment within the EU’s single market. This contributes to attracting investment and fostering sustainable economic growth, a key aspect of its effective operation.

Restrictions on member states’ regulatory autonomy in areas where sovereignty has been transferred to the supranational level extend to foreign economic activity. The EU’s “support concept,” however, requires clarification. While the EU’s external competence mirrors its internal competence in many areas, it’s not a simple reflection. The extent of EU competence in external relations is determined by the relevant treaties and varies depending on the specific policy area. The assertion of “exclusive competence” in all aspects of external economic relations requires further substantiation. While the EU plays a dominant role in trade negotiations (e.g., within the WTO framework) under its exclusive common commercial policy, as laid down in Articles 3(1)(e) and 207 TFEU (European Union, 2012c), the Member States nevertheless retain important competences, particularly in the field of Common Foreign and Security Policy, which remains largely intergovernmental and is governed by TEU provisions such as Articles 24 and 31 (European Union, 2012a). The EU’s intensive use of its external competence is largely true in economic spheres, but not universally applicable across all areas of external relations (European Commission, 2020, p. 5).

The EU’s common commercial policy eliminates Member States’ individual authority to regulate foreign economic activity. No preferential or exempted legal regimes can be granted to any third country, including Russia, once the common commercial policy falls within the Union’s exclusive competence under Articles 3(1)(e) and 207 TFEU (European Union, 2012c). This loss of national sovereignty in the field of trade policy and migration control was a key argument employed by Brexit proponents (Godovanuk, 2021, p. 10). Consequently, the UK now pursues aggressively liberal free trade agreements to circumvent the previously necessary balancing of interests with former EU partners (Godovanuk, 2021, p. 10).

To consolidate the transfer of sovereign powers to the supranational level, the EU has concluded a comprehensive network of trade, economic, and other agreements with numerous third countries. These agreements vary considerably in scope and form, depending on factors such as the third country’s economic development and pre-existing EU–Member State relationships. Examples include association agreements (e.g., Association Agreement with Georgia (European Union, 2014), partnership and cooperation agreements (e.g., Council of the European Union, 1997), and new-generation comprehensive free trade and investment protection agreements such as CETA with Canada and the Economic Partnership Agreement with Japan (European Commission, EU-Canada Agreement, 2021; EU-Japan Economic Partnership Agreement, 2020).

In order to secure the transfer of sovereign powers from the national to the supranational level and not allow individual member states to question it, the EU has concluded trade, economic and other agreements with almost all third countries. Depending on the type of country with which Brussels has been negotiating, its level of economic development, and the nature of the relationship that the EU and the Member States maintain with it, these may take the form of association agreements, association plus, partnership, and cooperation agreements (as with Russia), advanced partnerships, free trade, and investment protection, etc.

The European Union has recently pursued a new generation of comprehensive free trade agreements (FTAs), extending beyond mere tariff reductions to encompass legal convergence in various sectors. The FTAs with Canada (CETA), Japan (EPA) and the recently concluded agreement with MERCOSUR (European Commission, 2026) are widely regarded as significant foreign policy achievements of the Union, illustrating the growing breadth and ambition of its external economic policy (European Commission, 2021). This has led to significant expansions of EU powers in sectors such as banking, finance, budgetary matters and energy, as well as in the governance of the Area of Freedom, Security and Justice, as reflected in the post-crisis strengthening of economic and financial governance, the European Green Deal and related external action, and the Union’s evolving global role (e.g., Altenburg, 2024; Faus Onbargi & Malerba, 2024; Hackenesch, Keijzer, & Koch, 2024).

A defining characteristic of these FTAs is their treatment by the EU as integral to its internal legal order. Consequently, uniform application by all Member States and economic actors is mandated, enforced by the EU’s multi-level governance mechanisms. The Treaty of Lisbon concluded a long evolution of the EU’s legislative system, redistributing power between intergovernmental and supranational institutions. While the Council of the European Union initially held primary legislative authority, the European Parliament now plays an equally crucial, and in some instances, even dominant role, significantly impacting Member States and EU institutions.

The European Parliament has significantly influenced the EU’s policy agenda, particularly regarding climate change and taxation. Its lobbying efforts pressured the European Council, Council of the EU, and Member States to adopt more ambitious climate targets, exceeding the minimum obligations under the 2015 Paris Agreement and accelerating the implementation of a carbon border adjustment mechanism (CBAM) on imported goods (European Parliament, 2021). The July 2021 legislative package largely reflected the Parliament’s proposals (Krukowska & Ainger, 2021). Furthermore, the Parliament actively campaigned for enhanced measures to combat tax evasion and avoidance by multinational corporations (MNCs), advocating for a shift toward taxing corporate profits based on the location of economic activity rather than the company’s registered jurisdiction (Panayi, 2023, p. 240). This aims to curb tax dumping and increase state revenues. This advocacy aligns with the Parliament’s support for a digital services tax on large internet companies and the global minimum corporate tax rate of 15%, agreed upon by the OECD and G20 in 2021 and subsequently adopted by numerous countries, which has been closely followed and debated within the EU’s own corporate tax reform agenda (Panayi, 2023, p. 244).

In addition, the Parliament secured the establishment of a rule-of-law conditionality mechanism within NextGenerationEU recovery instrument. This mechanism, under which the European Commission is borrowing €750 billion for economic recovery (€390 billion in grants, €360 billion in loans), mandates Commission approval of national recovery and resilience plans, with funding contingent upon compliance with rule-of-law standards (European Union, 2020 2020/2092). The Parliament has actively monitored implementation, as demonstrated by its pressure on the Commission to extend the review period for Hungary’s €7.2 billion application, which was initially due by July 12, 2021 (Euronews, 2021).

The European Parliament’s increasing assertiveness, coupled with a perceived lack of effective accountability mechanisms for its members, is a source of growing concern among EU political elites and member state leaders. This situation, however, could be interpreted as evidence of a democratic transformation within the EU, suggesting the integration project now meets high democratic standards (Telo, 2014, p. 154). This assertion, however, overlooks the significant limitations—or even erosion—of democracy at the national level resulting from EU integration.

The EU’s constitutionalization is intrinsically linked to the elevation of human rights and fundamental freedoms to a central principle of its legal framework and operational functioning. Initially focused solely on economic integration, the EU recognized by the mid-1960s the impossibility of excluding human rights from the process. This led to a fundamental shift, with the EU actively promoting human rights as a core value, a dominant element of its socio-economic model, and a key component of its political system. Indeed, Brussels now advocates this human rights-centric approach as a standard for other states to emulate.

The European Union initially incorporated the European Convention on Human Rights (ECHR) and the constitutional traditions of its member states into its internal legal order without formally acceding to the ECHR. Subsequently, the Union adopted the Charter of Fundamental Rights, which expands significantly beyond the ECHR by encompassing a broader range of economic and social rights and eschewing the traditional generational classifications of human rights. The Lisbon Treaty elevated the Charter to the status of primary EU law, equating it with the founding treaties and granting it equivalent legal force since 2009.

Since the late 2010s, the principle of solidarity has emerged as a paramount legal principle underpinning the legitimacy of political and economic activities within the EU and its member states. This principle has received a broad interpretation. Its application has enabled the EU to assert the obligation of the Visegrad Four to implement a common immigration and asylum policy, including the redistribution of refugees among member states (see, e.g., European Council Decision (EU) 2015/1601 establishing provisional measures in the area of international protection for the benefit of Italy and Greece). This EU Council decision, adopted by qualified majority, was opposed by the Visegrad Four.

Furthermore, the invocation of economic solidarity as a supreme imperative of EU law led to the annulment, at Poland’s behest, of a European Commission decision concerning the partial exemption of the Opal gas pipeline (an onshore extension of Nord Stream I) from the Third Energy Package (General Court, Case T-883/16, Poland v. Commission, 2019). In July 2021, the Court of Justice of the European Union, upholding the General Court’s decision, rejected Germany’s argument that economic solidarity lacks legal substance, thereby definitively establishing its legal force (Court of Justice, Case C-848/19 P, Germany v Poland, 2021).

The concept of solidarity within the European Union has evolved into a flexible legal framework, enabling the EU to justify actions taken by the majority against individual member states (including Poland, Hungary, Cyprus, and even Germany) and third countries (including Russia). The Treaty of Lisbon allows member states to delegate additional powers to the EU, expanding its scope and altering decision-making processes without the need for formal treaty amendment via an intergovernmental conference and ratification. In certain instances, a unanimous European Council decision suffices (Vie publique, 2021; Toute l'Europe, 2020).

The approval of the NextGenerationEU recovery instrument, under which the European Commission borrows €750 billion on the markets (€390 billion in grants and €360 billion in loans), required ratification by 27 national parliaments in addition to the consent of the European Parliament, a process that lasted roughly a year. Conversely, the EU aims to achieve convergence of national tax systems and qualified majority voting in foreign policy, despite opposition from some member states, through a single unanimous decision of EU heads of state and government. This shift represents a significant departure from previous integration models, suggesting a de facto constitutionalization of the EU.

The EAEU’s Hybrid Dilemma: Sovereignty Safeguards vs. Integration Efficacy

Occupying a distinct and analytically crucial middle ground on the spectrum of legal institutionalization, the EAEU exemplifies a deliberate and innovative hybrid model. This section concentrates on the constitutional-like functions of the EAEU Treaty and the Union’s institutional safeguards for sovereignty, rather than providing a comprehensive political or economic narrative, in order to keep the analysis commensurable with the EU and ASEAN sections. Established in 2015 by the Treaty on the Eurasian Economic Union, the EAEU currently comprises Armenia, Belarus, Kazakhstan, Kyrgyzstan, and Russia. Its primary objective is to ensure the free movement of goods, services, capital, and labor, and to implement a coordinated or unified policy in key economic sectors to create a stable common market. This model consciously prioritizes the preservation of national sovereignty alongside economic integration, a design principle rooted in the unique geopolitical and historical context of the post-Soviet space, where concerns over dominance and a renewed loss of independence remain potent (Libman & Vinokurov, 2012, p. 58).

The Union’s foundational philosophy explicitly acknowledges that deep integration can only be sustainable if it is built upon a foundation of trust and unequivocal respect for the independence of its member states (Kembayev, 2009, p. 27). To this end, the EAEU’s architecture was thoughtfully designed with a suite of safeguards that directly address sovereignty concerns. These include a decentralized institutional structure centered on the Supreme Eurasian Economic Council (heads of state) and the Intergovernmental Council (heads of government), where the supreme decision-making power resides; a firm commitment to the principle of consensus (unanimity) on all fundamental issues, granting each member a de facto veto; a treaty-based focus on purely economic integration without explicit political overreach; and the deliberate avoidance of establishing a rigid, unconditional legal hierarchy that would automatically subjugate national legal orders (Eurasian Economic, 2014). These features are not oversights or signs of underdevelopment; they are the very pillars of a pact designed to ensure that integration is a voluntary and mutually beneficial process, rather than a source of friction or coercion (Petrov & Kalinichenko, 2016). From the perspective of the broad, functional understanding of constitutionalization employed in this article, the EAEU Treaty performs key constitutional functions: it establishes the Union’s legal personality, sets its objectives, creates a system of governance, distributes competences (exclusive, shared), and even enshrines the principle of the priority of its law within the scope of the transferred competences. However, this priority is not equivalent to the unconditional primacy of EU law and is explicitly contingent on proper implementation by member states, reflecting the hybrid nature of the construct.

At the same time, the EAEU’s legal order remains markedly heterogeneous when compared to the EU. While the Treaty on the EAEU codifies the free movement of goods, services, capital and labor, as well as the gradual establishment of common or coordinated policies in such areas as customs, technical regulation and competition, the degree of actual legal harmonization varies significantly across policy domains (Vinokurov, 2017). In some sectors, such as customs and tariff regulation, the Union has already developed a relatively dense set of common rules and practices that approximate a single market logic. In others, including energy, public procurement or financial services, the Member States retain extensive discretion and rely on intergovernmental coordination rather than supranational rule-making, resulting in a patchwork of partially overlapping national and Union-level norms. This internal differentiation is not accidental; it mirrors the political sensitivity of the respective areas and reflects a deliberate attempt by the drafters of the Treaty to calibrate the depth of integration in line with the varying degrees of domestic acceptance and strategic priorities of the participating states (Dragneva, 2017, p. 132).

This sovereignty-centric model, while politically astute and essential for the Union’s initial establishment and stability, presents a set of complex challenges for its operational efficacy and long-term development—a core dilemma at the heart of its hybridity. The consensus-based system, while protecting each state’s veto power, can lead to protracted negotiations, slow down decision-making, and hinder agile, collective responses to global economic shifts or internal market disruptions. The multiplicity of exemptions, transition periods, and the limited scope for robust, independent oversight of compliance by the Eurasian Economic Commission (the executive body) can lead to internal market fragmentation and inconsistencies in the application of common rules. The Court of the EAEU, while an important dispute settlement body, has a jurisdiction and authority more constrained than that of the Court of Justice of the EU, focusing largely on interpreting the Treaty and resolving disputes between member states on its application, with limited direct access for economic actors. Unlike the CJEU, the Court of the EAEU has only limited avenues for direct access by private parties and does not exercise a fully-fledged preliminary ruling procedure that would weave national courts into a dense judicial dialogue. Its decisions, although formally binding in the cases before it, have a more modest precedential effect and are less frequently invoked by domestic courts as authoritative guidance. As a result, the constitutional functions of the Court—such as stabilizing expectations, promoting uniform interpretation of Union law and gradually fleshing out the Treaty’s open-textured provisions—are only partially realized. The Union’s dispute settlement architecture thus operates primarily as a corrective mechanism for interstate conflicts, rather than as a daily driver of legal integration comparable to the central role played by the CJEU in the EU legal order (Karliuk, 2016, p. 13). This creates a paradox where the very mechanisms designed to protect the Union’s members from supranational overreach can also inadvertently weaken the very economic benefits—the seamless, predictable, and deeply integrated common economic space—that is the EAEU’s primary raison d’être. Consequently, the central challenge for the EAEU is to navigate this delicate balance: how to deepen integration, enhance the effectiveness of its common market, and strengthen its legal order’s coherence while remaining true to its foundational principle of respecting national sovereignty and its intergovernmental character (Petrov & Van Elsuwege, 2018). This tension manifests in debates over the need for more flexible decision-making procedures, greater powers for the Commission to monitor and enforce rules, and the development of a more unified legal practice.

The path forward for the EAEU, therefore, lies not in a wholesale adoption of any other model but in the strategic and selective adaptation of proven legal and institutional tools from more experienced integration schemes like the European Union, tailored to its specific context (Entin et al., 2021, р. 169). The goal is not federalization or the creation of a supranational polity but enhancing functional effectiveness within an intergovernmental framework. This involves a nuanced process of identifying specific mechanisms that can address the Union’s current operational challenges without altering its fundamental character. For instance, carefully calibrated moves toward qualified majority voting in specific, predefined technical areas (e.g., certain customs regulation details or sanitary standards), the strengthening of the Eurasian Economic Commission’s role in monitoring implementation and providing authoritative, non-binding recommendations, and the further development of a more coherent legal jurisprudence by the Court of the EAEU through its advisory interpretations could significantly enhance the Union’s functionality without perceived as a direct assault on sovereignty (Entin & Galushko, 2021, p. 493). The key to success is that any such adaptation must be done transparently and collaboratively, ensuring that new tools are viewed not as a power grab by a central authority but as practical, collectively agreed-upon solutions for achieving the collective economic goals outlined in the treaty. By embracing this pragmatic and evolutionary approach, the EAEU can solidify its unique position on the integration spectrum, demonstrating that a hybrid model of legal institutionalization can indeed evolve into a mature, effective, and resilient form of economic cooperation tailored to the specific needs, historical sensitivities, and aspirations of its members. Its experience illustrates that constitutionalization, in the broad sense, is a variable process where the degree of legal hierarchy and centralized enforcement can be consciously limited to sustain political consensus, even at the potential cost of optimal economic efficiency.

From a constitutionalization perspective, these challenges highlight the need for the EAEU to clarify more systematically the hierarchy of Union and national norms, to refine the catalogue of competences and to develop a more predictable practice of their exercise. Even without revising the formal principle of consensus, the Member States could agree on detailed procedural rules that limit the scope for unilateral blocking, for instance by introducing time-limits for negotiations, default rules in case of impasse, or pre-agreed criteria for derogations and transition periods. Similarly, the adoption of framework decisions or model laws at the Union level, followed by coordinated transposition at the national level, could strengthen the coherence of the common market while formally preserving national legislative sovereignty. Such instruments would not transform the EAEU into a supranational polity but would incrementally deepen its constitutionalization in the broad functional sense developed in this article, by rendering its legal order more structured, foreseeable and resistant to ad hoc political interference (Galushko et al., 2021).

The ASEAN Charter: A Constitutional Framework for Intergovernmental Cooperation

The ASEAN integration project stands in stark contrast to the EU’s supranational model and serves as a defining case at the intergovernmental end of the spectrum of advanced legal institutionalization. Its foundational philosophy is explicitly not the pooling or transfer of sovereignty but its staunch reaffirmation and protection. The idea of the ASEAN Community has its origin from more than four decades ago, until the adoption of the Declaration of ASEAN Concord II (Bali Concord II) in 2003 calling for the establishment of the ASEAN Community by 2020. Three pillars were envisaged, namely the ASEAN Political-Security Community (APSC), the ASEAN Economic Community (AEC), and the ASEAN Socio-Cultural Community (ASCC). This structure aimed to foster cooperation while meticulously preserving the core attributes of statehood (Mahbubani & Sng, 2017). The adoption of the ASEAN Charter in 2007 provided a concrete legal and institutional basis for this vision, realized with the formal establishment of the Community in 2015. The 2007 ASEAN Charter represents the cornerstone of this region’s unique constitutionalization process, understood in the functional sense defined earlier. Unlike the consolidated Treaty on European Union and the Treaty on the Functioning of the European Union, which in their post-Lisbon version operate as a de facto constitutional charter of the Union by establishing a hierarchical legal order characterized by primacy and direct effect, the ASEAN Charter functions as a framework treaty that codifies and reinforces an intergovernmental mode of cooperation rather than a supranational one. Its primary constitutional function, within the specific analytical framework of this article, is to codify the balance of power between the collective and its members, unequivocally prioritizing the latter and providing a stable, formalized shell for cooperation.

The ASEAN Charter specifies the relationship between the Community and the Member States in the first place through the principle of respect for the independence, sovereignty, equality, territorial integrity and national identity of all Member States (The ASEAN Charter, Article 2(2)(a)). This principle is further demonstrated in other principles, including the one on non-interference in the internal affairs (Id., Article 2(2)(e)). In the meantime, the Charter also emphasized the importance of the centrality of ASEAN in external political, economic, social and cultural relations (Id., Article 2(2)(m)). Accordingly, the Charter strikes a balance between the Community and the Member States regarding internal and external affairs. This creates a deliberate equilibrium: internally, the sovereignty of member states is absolute and non-interference is paramount; externally, ASEAN aspires to act as a cohesive and central actor. This delicate balance defines the very essence of ASEAN’s constitutional identity within the integration spectrum. The institutional architecture established by the Charter faithfully reflects this intergovernmental logi. While being an intergovernmental organization, the ASEAN Community is not a supranational entity at its current status; consequently, the ASEAN Coordinating Council took up the role in coordinating the external policy at the community level. Like any other constitutional documents, the ASEAN Charter plays two roles in providing operational framework and rights and duties of relevant parties. With regard to the operational framework, the Charter establishes organs for the proper function of the Community; apart from the Coordinating Council, such organs include ASEAN Summit, Community Councils in the fields of three pillars, Sectoral Ministerial Bodies, Secretary-General and Secretariat, Committee of Permanent Representatives, National Secretariats, Human Rights Body and ASEAN Foundation. Concerning the rights and duties of relevant parties, the Charter provides rules on immunities and privileges of ASEAN, the Secretary-General and Secretariat, the Permanent Representatives and Officials on ASEAN duties. As a non-supranational entity, ASEAN lacks institutions with independent law-making or direct enforcement authority akin to the European Commission or the CJEU. Decision-making remains firmly rooted in consultation and consensus (musyawarah and mufakat) among member states. Taken together, these organs do not amount to a supranational machinery comparable to the Commission-Council-Parliament triangle in the EU, yet they perform a distinct constitutional function in the ASEAN context. By conferring a certain degree of continuity and bureaucratic memory upon what used to be an almost entirely intergovernmental and summit-driven process, the Secretariat, the Committee of Permanent Representatives and the various Community Councils help to stabilize expectations, standardize procedures and provide low-key forums where compromises can be crafted away from the spotlight of high politics (Caballero-Anthony, 2008). In this sense, the Charter’s institutional blueprint constitutionalizes not power-transfer, but process: it entrenches the habit of structured consultation and regularized interaction among national administrations. This incremental, procedural form of constitutionalization is particularly suited to a regional environment where domestic political systems are highly diverse and where many governments remain wary of formal constraints on policy discretion. The purpose of ASEAN’s institutions is to support and facilitate member-state-driven processes, not to override or dictate to them (Mahbubani & Sng, 2017).

The codification of the principles of sovereignty and non-interference in the ASEAN Charter should be understood against the backdrop of the Association’s earlier practice, where these norms were predominantly articulated in political declarations, joint communiqués and summit statements. By elevating them into a treaty-level instrument, the ASEAN states sought both to reassure domestic audiences that deeper institutionalization would not undermine their core statehood prerogatives and to signal externally a stronger commitment to act collectively on the regional stage (Ba, 2014). Yet, this constitutionalization of non-interference simultaneously constrains the Community’s capacity to respond to internal crises—ranging from democratic backsliding and human rights violations to maritime security incidents—because any robust joint action is politically perceived as a potential encroachment upon national autonomy. The Charter thus embodies a paradox: it is an integration instrument that constitutionalizes the very principles that traditionally justified a preference for loose, informal cooperation.

Consequently, the adoption of the ASEAN Charter signified the start of a new era for the ASEAN in its further integration process; the document per se serves not only as a legal basis for the integration in the region, but also as a constitutional framework for the proper and sustainable functioning of the Community in the years to come. The ASEAN integration process provides a vivid example of the constitutionalization of integration legal orders through the adoption of an instrument, but of a distinct kind. It represents a pragmatic and primarily symbolic form of constitutionalization, where the constitutional framework is designed to facilitate and structure voluntary cooperation without compelling deep legal integration or demanding sovereignty concessions. It provides a formal legal basis for community-building, a structured dialogue platform, and a sense of collective identity, yet it consciously stops short of creating a supranational legal order with direct effect and primacy. The economic dimension further illustrates this point. The ASEAN Economic Community (AEC) Blueprint and its subsequent iterations lay down ambitious objectives of creating a single market and production base, but implementation remains highly uneven across sectors and member states. Tariff liberalization has progressed significantly, whereas behind-the-border barriers, investment restrictions, services liberalization and labor mobility continue to be treated with caution and subject to numerous reservations. The Charter and the AEC instruments therefore operate as a constitutional shell that provides political endorsement and a general legal framework for economic integration, without embedding hard, court-enforced obligations comparable to those found in EU law. In practical terms, ASEAN’s constitutionalization primarily facilitates policy coordination and peer pressure rather than judicially enforceable rights for economic actors, placing it clearly at the soft-law and intergovernmental end of the spectrum.

The ASEAN model demonstrates that constitutionalization, in the broad analytical sense employed here, is not synonymous with federalism or supranationalism. Instead, it can serve to strengthen, formalize, and provide a normative foundation for an intergovernmental system, offering a stable constitutional shell for cooperation that is entirely voluntary and consensus-based. This places ASEAN at a definitive point on the spectrum of regional integration, showcasing how foundational legal instruments can be adapted to a context where the preservation of absolute sovereignty is the paramount principle, thereby achieving a form of institutional consolidation tailored to the region’s specific political and historical context.

Constitutional Tools for Regional Integration: Opportunities and Adaptive Pathways

The comparative analysis of the EU, EAEU, and ASEAN reveals that the process of constitutionalization reflects a spectrum of integration models, each with distinct implications for sustainable development and effective governance. These models can be broadly categorized into supranational (EU), hybrid (EAEU), and intergovernmental (ASEAN) types, distinguished by the extent of sovereignty delegation, the legal supremacy of common norms, and the robustness of enforcement and dispute resolution mechanisms (Acharya, 2016). The foundational treaties of these entities are not merely static agreements but living constitutional instruments that play a pivotal role in their integration processes, defining their legal personality, operational structures, and the perpetual balance between collective authority and national sovereignty (Alter, 2021). The choice and calibration of specific constitutional tools embedded within these frameworks are crucial for addressing functional challenges and enhancing the entity’s capacity to ensure long-term sustainability and effective operation.

At the supranational level, the EU represents the most legally consolidated paradigm. The Treaties on European Union and on the Functioning of the European Union, as amended by the Treaty of Lisbon, function de facto as a constitutional charter, establishing a hierarchical legal order characterized by the primacy and direct effect of EU law (European Union, 2007). This framework enables uniform application and is enforced through a robust, centralized judicial system centered on the Court of Justice of the European Union (CJEU), which ensures consistent interpretation and resolves conflicts between national and supranational norms (Stone Sweet, 2018). The EU’s constitutional toolkit is dynamic, featuring mechanisms like “passerelle clauses” that allow for deeper integration in specific areas without formal treaty amendments, thereby providing flexibility (Pech & Kochenov, 2021). This advanced institutionalization has allowed the EU to expand its competences into areas such as human rights, economic governance, and foreign policy, fostering a shared identity underpinned by principles like solidarity and the rule of law (Schimmelfennig, 2018). However, this model also demonstrates the inherent risk of sovereignty-backlash, as illustrated by Brexit, highlighting that excessive centralization can threaten the perceived legitimacy and, consequently, the sustainability of the integration project.

In contrast, the EAEU operates with a deliberately constrained hybrid model. Its founding treaty is a pragmatic compromise, blending elements of supranational economic integration—such as the principle of supremacy of Union law within its conferred competences—with robust intergovernmental safeguards, most notably a persistent reliance on unanimity for key decisions (Dragneva & Wolczuk, 2017). This reflects a strategic choice to prioritize sovereignty and avoid the EU’s level of political union. Consequently, its constitutional framework is more decentralized, with limited independent oversight mechanisms and a primary focus on economic rather than political integration (Vinokurov, 2017). For the EAEU to enhance its efficacy and the seamless functioning of its common economic space—key to its sustainable development—it need not pursue federalization but can selectively adapt proven constitutional tools. Opportunities lie in carefully calibrated steps, such as introducing qualified majority voting in specific technical areas (e.g., technical regulations), strengthening the Eurasian Economic Commission’s mandate for monitoring compliance and facilitating implementation, and fostering a more coherent jurisprudence from the Court of the EAEU to ensure predictable interpretation of common rules (Entin et al., 2021; Entin & Galushko, 2021). The strategic adoption of such tools, if done transparently and consensually, can address operational challenges like market fragmentation and slow decision-making, thereby solidifying its economic raison d'être without compromising its foundational sovereignty pact.

At the intergovernmental end of the spectrum, ASEAN’s constitutionalization is expressly symbolic and sovereignty-centric. The ASEAN Charter emphasizes absolute respect for national sovereignty and non-interference, establishing a framework for cooperation based on consensus and soft governance (Acharya, 2017). It lacks supranational enforcement mechanisms and the primacy of ASEAN law, with institutions like the ASEAN Coordinating Council playing coordinating rather than authoritative roles (Jetschke & Murray, 2012). The Charter’s constitutional function is thus primarily to provide a normative foundation for regional identity and a structured dialogue platform, not to impose a hierarchical legal order (Tan, 2011, p. 45). For ASEAN, the path to greater effectiveness may involve incremental hardening within its intergovernmental paradigm. This could include strengthening existing dispute settlement mechanisms in economic agreements, enhancing the capacity of the Secretariat for monitoring and reporting, or developing more precise rules for implementation within the consensus framework. The goal is not to become supranational but to increase the reliability and depth of cooperation, addressing challenges like the “consensus stagnation” noted by scholars (Jones, 2010), thereby improving its operational effectiveness while maintaining its core philosophy.

The constitutional documents of these entities are thus instrumental in shaping their integration trajectories and capacities for effective operation. In the EU, the Treaty of Lisbon acts as a dynamic engine for progressive centralization. For the EAEU, its treaty is a flexible compromise, offering enough structure for economic integration while accommodating sovereignty concerns. ASEAN’s Charter reflects a minimalist approach, prioritizing flexibility and voluntary cooperation (Acharya, 2009). These differences underscore that constitutionalization is not a uniform process but a spectrum of possibilities shaped by distinct political, economic, and historical contexts. The opportunities for enhancing integration lie in the strategic, context-sensitive adoption of constitutional tools. A key prospect for entities like the EAEU and ASEAN is the establishment of more effective dispute resolution mechanisms to mitigate legal fragmentation and enhance compliance predictability, moving away from sole reliance on political bargaining. Another is the gradual expansion of institutional competences to address emerging cross-border challenges (e.g., digital trade, sanitary measures, or logistics corridors) through treaty protocols or enhanced mandates for executive bodies, as seen in the EU’s adaptation to banking and energy crises (Fabbrini, 2019). Economic integration, a common goal, can be deepened through tools like regulatory harmonization, mutual recognition agreements, and the reduction of non-tariff barriers, all of which require a certain degree of legal institutionalization to be effective.

Ultimately, the critical challenge for all regional integration entities is balancing the functional benefits of advanced legal institutionalization with the imperative of preserving member state sovereignty. Hybrid and differentiated approaches, such as “opt-out” clauses or variable geometry in integration, offer potential pathways (Leuffen et al., 2013). The experiences of the EU, EAEU, and ASEAN demonstrate that there is no one-size-fits-all model. Sustainable development and effective operation are achieved not by the triumph of one constitutional paradigm but by the continued, diverse, and adaptive application of legal and institutional tools that resonate with the specific levels of integration, political comfort, and shared aspirations of the member states within each unique regional context.

Conclusion

Following the trend of globalization and technological development in the early 21st century, the international community is becoming increasingly interconnected, catalyzing deeper integration at international and regional levels. This integration process frequently manifests a formal constitutional element through the adoption of foundational legal instruments. The conducted research has demonstrated that the process of advanced legal institutionalization and consolidation—examined through the broad lens of constitutionalization—is a significant and defining process for international entities seeking sustainable development and effective operation. However, as the comparative examination of the EU, the EAEU, and the ASEAN reveals, this process forms a spectrum, not a binary state. Its specific character is profoundly shaped by the unique political, economic, and historical context of each region, reflecting a constant negotiation between the impulse for collective action and the imperative of preserving national sovereignty. The sustainable development and effective functioning of these entities are intrinsically linked to their capacity to institutionalize their legal orders in a manner that provides stability, predictability, and mechanisms for resolving conflicts, thereby fostering an environment conducive to long-term cooperation and growth.

The EU stands as the most advanced paradigm of supranational constitutionalization within this spectrum. Its foundational treaties, particularly the Treaty of Lisbon, function as a de facto constitution, establishing a hierarchical legal order characterized by the primacy and direct effect of EU law, a powerful judicial enforcement mechanism, and an ever-expanding scope of competences facilitated by tools like the passerelle clauses. This model, while highly effective in fostering deep integration and a stable single market, also carries the risk of provoking sovereignty-based backlash, as evidenced by Brexit, highlighting the perpetual tension at the core of the integration project. In stark contrast, ASEAN embodies the intergovernmental end of the spectrum, where constitutionalization remains largely symbolic and framework-oriented. The ASEAN Charter prioritizes absolute respect for sovereignty and non-interference, creating a foundational document for cooperation based on consensus and soft governance rather than legally binding supranationality. Its constitutional function is to codify intergovernmentalism, providing a stable platform for dialogue and incremental cooperation without compelling integration.

Occupying a deliberate and innovative hybrid middle ground, the EAEU’s constitutionalization is tentative and consciously circumscribed. Its founding treaty is a pragmatic compromise, blending elements of supranational economic integration—such as the principle of supremacy of Union law within its competence—with robust intergovernmental safeguards, most notably the persistent reliance on unanimity for key decisions. This reflects a strategic choice to avoid the EU’s level of political union while actively aspiring to build a cohesive economic space. Consequently, the most instructive comparative models for the EAEU’s future development may not be the fully-fledged supranationalism of the EU alone, but rather a selective learning process that also considers the flexible, sovereignty-centric approach of ASEAN, albeit with a greater inherent potential for legal hardening in the economic sphere.

The prospects for these entities lie in the strategic, context-sensitive adoption and adaptation of constitutional and quasi-constitutional tools. For the EAEU and ASEAN, this does not necessitate a wholesale imitation of the EU’s model. Rather, it involves selectively adapting its technical mechanisms—such as strengthened independent dispute resolution, carefully calibrated moves toward qualified majority voting in specific technical areas, and the harmonization of regulatory standards—to their own levels of integration, political comfort, and functional needs. The key challenge for all integration projects remains finding a viable and dynamic equilibrium. The EU must continually legitimize its centralization of authority and manage differentiation, the EAEU must build sufficient mutual trust to enable deeper and more efficient delegation for the sake of common market efficacy, and ASEAN must navigate the inertia of its consensus model to enhance its collective effectiveness and resilience.

The EU, as a supranational entity, and the ASEAN Community represent different degrees and philosophies of integration at the regional level. While both adopted international instruments defining their legal personalities, they, respectively, designed their institutional architectures and internal functioning to fit their distinct goals and political realities. The EAEU has the benefit of observing both examples in its ongoing integration process, aiming to design a framework suited to its own goals, principles, and operational parameters. The cases of the EU, ASEAN, and the EAEU in their integration processes justify the importance of a deliberate and coherent process of a broad constitutionalization to ensure their proper operation and sustainable development. This phenomenon further demonstrates and serves as a vivid comparative example of the multifaceted constitutionalization of the international legal order.

Ultimately, the foundational documents of these entities are living instruments. They are both the product of their current political reality and the framework for their future evolution. They do not merely describe a static legal order but actively constitute a dynamic process of integration, constantly being shaped by and shaping the interplay of law, politics, and regional identity. The future of international integration will therefore be written not by the triumph of one constitutional model over others, but by the continued, diverse, and context-specific adaptation of constitutional principles and legal-institutional tools to meet the distinct challenges and aspirations of regions around the world. The spectrum of constitutionalization, from the supranational to the intergovernmental, provides a vital analytical framework for understanding this ongoing global transformation. The cases of the EU, ASEAN, and the EAEU in their integration processes justify the importance of a deliberate and coherent process of a broad constitutionalization to ensure their proper operation and sustainable development. In empirical terms, the EU illustrates how far-reaching supranational constitutionalization can underpin a dense single market while generating sovereignty-related tensions; the EAEU shows the advantages and costs of a sovereignty-protective hybrid model; and ASEAN demonstrates that even a symbolically constitutional, consensus-based framework can provide a durable, if limited, platform for cooperation. These findings jointly confirm that there is no linear hierarchy among integration models, but rather context-specific trade-offs along the sovereignty–integration spectrum.